“There were a lot of good linebackers out there this year,” 49ers general manager John Lynch said of the available free agents. “Kwon, I think I’ve long admired. I believe certain players bring out the best in their teammates with the way they play. There’s a certain passion for the game that screams even when you’re watching film that’s silent. You can just see it jump through. And he plays with his hair on fire, and I think that kind of play is contagious. We needed that. He’s also extremely productive.”

Alexander became an immediate starter in the middle of Tampa Bay's defense after joining the Bucs from LSU in the fourth round of the 2015 NFL Draft. He led the NFL in solo tackles with 108 in 2016, and he earned an invitation to the Pro Bowl in 2017.

During Alexander's first two seasons with Tampa Bay, current San Francisco coach Kyle Shanahan served as the Atlanta Falcons' offensive coordinator, so they squared off twice annually as NFC South rivals.

“He taught me a hard lesson that you better game-plan for him, because I didn’t too well,” Shanahan said. “First game of 2016, we started out 0-1 because of it, and I remember him having 20 tackles -- or maybe 16 or 18 -- but it was bad. It was so bad that (wide receiver) Julio (Jones) asked me after the game if he could play fullback and block him. I knew I needed a better plan the next time.”

“I’m just taking it day-by-day,” Alexander said. “I’ve just been grinding, working hard and just pushing myself to get back. I’m just taking it day-by-day, let it all work out for itself and I’ll be back soon.”

The middle linebacker for the Buccaneers, Alexander could wind up playing weakside linebacker for the 49ers.

“Wherever they want to put me at, I’m going to work my hardest and do whatever I can to get wins under our belt,” Alexander said.

While his position on the field may still be determined, Alexander wants to have a well-defined role in the San Francisco locker room.

“We’re going to try to make sure those guys are on point, studying film, have the same mindset to be great,” Alexander said. “I’m going to tell them, ‘Whatever it takes. Whatever it takes, you can do it. Put your mind to it, we’re going to go out here and get the job done.’”

Alexander was an Under Armour All-American at Oxford in 2011. He was an honorable-mention All-State pick as a sophomore and junior before missing most of his senior season with a knee injury.

The 49ers' inside-linebackers coach DeMeco Ryans is a Bessemer native who played at Alabama.

“I was watching him when he was coming out of college at Alabama,” Alexander said. “I can’t wait to pick his mind. He’s going to help me a lot.”

Alexander wore No. 58 with Tampa Bay. The 49ers already have a No. 58 -- center Weston Richburg -- and Alexander can’t wear his high school number (17) or college number (4) because those are off-limits for NFL linebackers. So Alexander said he’ll wear No. 56 for San Francisco.

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